1. Field of the Invention
This invention relates to a dispensing device which is suitable for the dispensing and administration of a metered amount of powder. Such a device would be suitable for the dispensing and administration of pure powder form drugs or drugs mixed with a suitable carrier agent, e.g. lactose.
Metered dose inhalers are well known and often comprise a pressurized aerosol dispensing container. The aerosols contain gas propellants in which the powdered medicament is suspended. Upon actuation, the aerosol contents are expelled, through a metering valve, and a metered dose is propelled into the lungs of the patient.
Research has indicated that some aerosol propellants, including those used in metered does inhalers, can cause depletion of the ozone layer in the atmosphere. It has thus become more important that such inhalers can be substituted with metered dose inhalers which do not have a damaging effect on the environment. Furthermore, such aerosol systems are not suitable for some patients.
2. Description of the Prior Art
Several types of powder inhalers are known. Usually a metered dose of medicament is initially contained in a container. The container is often in the form of a gelatin capsule. The capsule is first opened, such as by piercing with a pin, and then its contents are dispersed and expelled by ensuring that airflow, due to the inhalation of the patient, causes the capsule to rotate.
These powder dispensers have several disadvantages. It is necessary for the patient to reload the dispenser after each dose release, and in some devices the capsules must be pierced before loading. Complicated mechanisms are employed to ensure complete expulsion of powder in order to provide the correct dose to the patient. This can make the devices difficult to operate and expensive to manufacture.
GB 2102295 and GB 2144997 disclose a complicated inhaler in which a metered dose of medicament is dispensed from a storage chamber containing powdered medicament in a pelletized micronized form. The inhaler includes a dosing unit which is connected to a storage chamber for the medicament. The dosing unit comprises a perforated rotating membrane, and spring loaded scrapers to fill the rotating perforations with medicament. The filled perforations are introduced to a passage which connects a propellant container to a nozzle. An amount of propellant is released when the patient depresses two triggers in succession. The propellant expels the contents of the exposed perforations towards the nozzle to be inhaled by the patient. The size of the metered dose is determined by the size of the perforations and the number of perforations that are brought into the propellant passage.
Such a device is expensive to manufacture, and the dosage accuracy relies on the efficiency of the scrapers to fill the perforations. The perforations often need to be presented several times to the powdered medicament to ensure complete filling. For optimum effect the device also requires the patient to coordinate inhalation with the operation of propellant release. Many patients find this coordination difficult to achieve.
EP 0069715 discloses a device which attempts to overcome some of the aforementioned problems. There is disclosed a powder inhaler which is actuated by the airflow generated by the inhalation of the patient. A breath actuated device eliminates the problem of the coordination of manual actuation and inhalation. A propellant is no longer necessary to effect actuation. The device also uses a perforated membrane and spring loaded scrapers to provide a metered dose of medicament. The patient rotates a maneuvering unit by a certain amount. This rotates the perforated membrane with respect to the scrapers filling the perforations and exposing a certain number of them to an air passage. The air flow generated on inhalation passes through the perforations and the metered dose is inhaled by the patient. A rotating means is provided to disrupt the airflow so as to break up any aggregate particles which have been formed in the dosing unit.
This device has the disadvantage that the airflow generated on inhalation passes directly through the perforations which are then returned to the dry storage chamber for refilling. Any powder which has become lodged in the perforations may become contaminated by the air, and this is then mixed with the pure dry powder held in the chamber. If the perforations become partially blocked then a full dose of medicament will not be inhaled by the patient.